She Just Had to be His Sister
by LovelyLoreley
Summary: After Gideon leaves the Lightwoods, his brother Gabriel comes to see him at the Institute. There he meets the haughty, demanding, reckless Cecily Herondale. Gabriel/Cecily Tessa/Jem
1. Chapter 1

Gabriel huffed as he jumped down from the Lightwood carriage and slipped through the gates of the Institute. He would rather have been anywhere else, but Father had insisted he come and bring Gideon home. Not that Gideon would listen to him; Father knew that as well as Gabriel did.

So why was he there? It was a lost cause anyway, right? Gabriel couldn't deny it, though. He had missed his brother these past two weeks.

At any other time, Gabriel would have just barged into the Institute and demanded to be taken to Gideon. Something stopped him this time, and he rang the brass bell reluctantly, fidgeting with his collar as he waited.

A young man opened the door and looked at him in fain surprise. "Mr. Lightwood. I presume you are here to see your brother." It was not a question. Gabriel tried to remember the man's name. Thomas? No, that had been his brother. This one was Cyril.

Gabriel was about to reply when he heard a female voice. "Cyril? Who is it? Charlotte isn't expecting anyone – oh." Tessa came around the corner and caught sight of Gabriel. "Gideon's in the training room, I believe. I'm sure you could find your way there without my help, but…I'll walk with you," she offered. Gabriel nodded mutely, unwilling to speak to her.

They set off down the corridor and Gabriel snuck a sideways glance at Tessa. She was just as beautiful as the day he had first met her. Her brown curls were escaping her bun, framing her face with wispy tendrils. If she had been a Shadowhunter, he might have pursued her. As it was, what with Tessa being a Downworlder, such a thing would only liken him to Father's reputation.

"Why aren't you training with them?" Gabriel asked Tessa, noting that she wore a dress rather than her black training pants. He assumed that he would find his brother with the servant girl, Sophie.

"My old mentor just sort of up and dusted – um, ran off," Tessa clarified, giving Gabriel a meaningful glance. "And Jem's out on business today."

"Carstairs? He's been training you?" Gabriel asked in surprise, thinking of the sickly, silver-eyed boy.

"Well, yes. He's been worrying about my safety ever since the proposal. He thought it prudent to continue where you left off."

"Proposal? What proposal? Carstairs proposed to…you?"

"Oh – um, yes, he did. Jem and I have been engaged almost two weeks now." Tessa said, grinning at him and blushing. "He's been teaching me defense when he has the time, but he has other things to attend to as well."

"Does the Clave know about the two of you?"

"Oh, yes. At present they aren't quite sure just what to do about it. Without a warlock mark they can't exactly call me an illegal bride. Jem thoroughly enjoys our being an anomaly."

"But are you not worried that they will end up deciding that your union is illegal? You are after all, most likely a Downworlder…"

"Oh, I'm sure he's thought about it." Tessa stopped and looked around warily. They stood outside the training room. "Don't tell him I said this, because I don't think he would want me to know, but I believe if it comes to that he tends to play his illness card. If he is to die soon anyway, our union will not cause any harm." She turned away abruptly.

"I am sorry," Gabriel muttered after a pause. "This must be hard for both of you, knowing that your time together is so short."

"I know no such thing," Tessa retorted, reaching for the door handles. "We could always find a cure."

_And even if you find a cure, what then, Tessa? Then they will tell you that you are not fit for a Shadowhunter. Either way your happiness is short-lived,_ Gabriel thought. He followed Tessa into the training room.

Gideon was there, along with two females. One of them Gabriel recognized as Sophie; the other looked vaguely familiar but Gabriel was certain he had never seen her around the Institute.

"Brother," Gideon said, straightening from his position against Sophie's back. Sophie lowered the knife in her hand and gazed warily at Gabriel. "Gabriel, what brings you here?"

"What do you suppose? Father wanted me to come and demand that you return home. I know your answer already, Gideon, there is no need to frown at me in that manner."

"If you knew my answer then why did you come?" Gideon demanded, standing protectively in front of the two girls. Tessa remained next to Gabriel, watching curiously.

"You know Father. He will not take no for an answer, though I have tried to convince him. I also wanted to make sure that you were kept here in hospitality rather than in the dungeons."

"Oh, don't be ridiculous Gabriel!" Tessa protested. "There aren't any dungeons in the Institute!"

Gideon, on the other hand, cracked a rare smile. "Believe it or not, Miss Grey, my brother was actually joking. I know he doesn't exactly seem like the kidding type, but there you have it. He has a dark sense of humor, really."

"Well, and he wouldn't be the only one around here, would he?" The unfamiliar girl spoke up impatiently, flicking tendrils of silky black hair out of her startling blue eyes. "Gideon, perhaps you'd like to introduce me to this brother of yours?"

"Oh of course, my apologies." Gideon grinned ruefully. "Miss Cecily, this is my brother Gabriel. Gabriel, may I introduce Miss Cecily –"

"Oh, don't tell me," Gabriel groaned, realizing a split second before Gideon said her name why she had looked familiar. "You're that dratted Herondale's sister, aren't you?"

"And what if I am?" Cecily demanded haughtily. Gabriel could only shake his head in annoyance and exasperation.

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_**Yes this is a Gabriel/Cecily pairing with a bit of Jessa and possibly other couples thrown in. I began to write this piece in response to all the Wessa shippers who really really want Jem to leave Tessa for Cecily. I do NOT think that will ever happen, and I think this pairing is much more likely and I really like the idea of it happening.**_

_**Review and Favourite please, if you want me to continue. I update the stories that get reviewed. So let me know if you want it continued!  
**_

_**Mwah! ~Loreley**_


	2. Chapter 2

Cecily glared at Gabriel, her silence demanding an explanation. _Maybe if I treat you the way he treated my sister, you would understand,_ Gabriel thought bitterly, but that would never do. Something about Cecily made Gabriel think that a general dislike of the elder Herondale was something the two of them had in common.

"Nothing," he finally muttered. "I just thought you looked familiar, that's all." Gideon raised an eyebrow in surprise as Tessa let out a cough that Gabriel was sure covered a laugh.

"If that was all, why did you call my brother dratted?" Cecily demanded, but the small smile that lifted the corners of her mouth contradicted her sharp words. Gabriel shrugged, knowing that both Gideon and Tessa were still laughing silently. Cecily let out a short laugh as well, glancing over her shoulder at Gideon and Sophie. "It's okay; I know how much of a bother he can be. He annoys me as well!" Even Sophie cracked a smile at that, although she looked uncomfortable in the present company, as though she thought the room might explode into violent action at the slightest provocation.

At that moment the door creaked open behind Gabriel, and he spun around to see Jem enter the room. The silver-haired boy acknowledged Gabriel with a small nod and went to wrap his arms around Tessa's waist. "Hello, Gabriel," Jem greeted him. "I was told I would find you and Tess up here. Would you mind stepping into the hall for a bit? I wanted to speak with you."

Gideon and the girls watched curiously as Gabriel followed Jem out of the training room. Out in the hall, Jem strode quickly around the corner and into a sitting room with bookshelves and a blazing fire. He gestured for Gabriel to take a seat and walked to stand before the window, his back to the room. Gabriel sat cautiously.

"Before you ask, I am not sent here by Charlotte. In fact, she does not yet know that I have returned home from my errands. I only wanted to know," he continued, turning around and striding to a seat facing Gabriel, "how is your father faring? And yourself? I know it must be hard –"

Gabriel snorted. "Of course it's hard! Your dear Charlotte has put our family in very dire straits and soiled our name to boot. Father must stand before the Clave…and we all know what will come of that…"

"Well, and can you blame them?" Jem cried leaning forward. "Gabriel, your father is not the respectable Shadowhunter we all thought he was. To dally with demons! And then to have infected and killed his own wife! It is a serious matter, indeed. And if you truly know the consequences of standing beside him, then perhaps my offer may not be in vain. As you know, your brother is safe from the stain of your father by his residence here at the Institute. If you would rather restore honor to your name than be stripped of your marks, you would always be welcome here as well, you know."

Gabriel snorted again, not bothering to hide his disgust. "Oh I'm sure you mean that truly, Jem. That you would welcome me I have no doubts. But as for others –"

"Your brother would like to have you here," Jem interrupted firmly. "He worries about you. And I know you could hardly care what the servants think of you. Tessa will accept it in a heartbeat as long as I trust you, which I do. And you've only just met Cecily, so I doubt her opinion means more to you than Sophie's. Charlotte and Henry don't really mind much at the moment if it doesn't directly concern them and the naming of their child, but in general they love having to care for us.

"That leaves only Will as a possible dissenter, and he doesn't spend much of his time here anyway. It may be hard to believe, but he has always been just as unpleasant to the rest of us as he seems to you, and we've been able to put up with him. I think you would find it quite easy."

Jem stood, looking down at Gabriel thoughtfully. "I hope you will at least consider my offer. You do not have to speak of it anymore today, if you wish, but know that you only have so much time to make a decision. Good Shadowhunters are rare these days, and I would hate to see one turned mundane on a matter of pride." He turned to leave.

"Wait!" Gabriel stood. "You really intend to leave me here with no escort out?"

Jem raised one eyebrow. "Do you need an escort? My apologies; I assumed you had been here so many times that you quite knew your way around the place."

"Of course I could find my own way out!" Gabriel cried indignantly. "I only meant to ask whether you really thought I wouldn't try anything in your absence."

"Were you listening to a word I just said?" asked Jem incredulously. "Your heart is in the right place; I can tell, and I trust you because of it. We have no secrets that would help your father out of his current situation, and I just offered you safe haven here. Trying to sell us out would be not only rude, but also stupid on your part. And you are not a stupid boy."

Gabriel sat frozen in his seat as Jem closed the door. He didn't know how long he sat there, letting an unknown feeling of gratification steal across his heart. Gideon was safe in these people's hands and they were kind enough to extend those hands in friendship even to one who had blatantly criticized them.

Eventually he stood and stretched, ready to return home to his father and give him news of Gideon. He had his hand on the doorknob when he heard voices in the hall raised in apparent anger. He paused, unwilling to come in the middle of an argument.

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**Okay I know, this is a really weird, bad place to stop. I meant to include more in this chapter but that would have made it really long as Jem spoke more than I thought he would. This wasn't meant to be a sort of pseudo-cliffhanger, I swear. Read, review, and favourite and I will try to post the next chapter soon!**


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